Malaria transmission entails development of the Plasmodium parasite in the mosquito. An understanding of not only protein-protein but protein-glycan interactions are needed before we can completely dissect the molecular mechanisms involved in Plasmodium ookinete invasion of the mosquito midgut. Objectives: This is a proposal to assess the role of protein-glycan interactions during Plasmodium ookinete invasion of the midgut. To do so, we aim to further identify and characterize mosquito midgut glycan ligands and the protein core(s) to which the glycans are attached. We will then identify the cognate lectin-like receptors on the ookinete and characterize their functional role in vivo. Research Design: The research plan includes: a) functional analyses of mosquito midgut glycoconjugates during Plasmodium invasion through RNAi knock-down of mosquito glycosyl- and sulfo-transferases, b) proteomic identification by mass spectrometry of mosquito coretin gene knockout lines). Cellular glycosyltransferases are involved in posttranslational and co-translation modification of proteins. As proof of principle, by RNAi, we were able to diminish enzymatic activity of the primary midgut glycosyltransferase involved in initiating glycosaminoglycan (GAG) biosynthesis on polypeptides. This resulted in >90% inhibition of parasite development in the mosquito. We also provide evidence for the use of lectin-affinity chromatography followed by tandem mass spectrometry to identify glycoproteins that are recognized by specific lectins. Conversely, we anticipate that the process will be successful in identifying lectins that can bind to defined glycan moieties. Lastly, we propose to produce lectin gene knockout lines and assess the midgut invasion phenotype in vivo. Summary: An effective malaria vaccine remains elusive. The characterization of these mosquito ligands and parasite receptors offer us additional target antigens toward the development of malaria transmission-blocking vaccines and provide us critical insight into parasite and midgut cell biology and vector host-parasite interactions. 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